Air conditioner

ABSTRACT

An air conditioner having in a refrigeration cycle a fixed displacement-type first compression mechanism and a variable displacement-type second compression mechanism independent from each other, and also having second compression mechanism displacement control means, compression mechanism operation switching control means, an evaporator for refrigerant, a condenser, a blower, evaporator temperature detection means, and evaporator target temperature calculation means. The evaporator target temperature calculation means has first compression mechanism evaporator target temperature calculation means for calculating a target temperature for the first compression mechanism and second compression mechanism evaporator target temperature calculation means for calculating a target temperature for the second compression mechanism. When the refrigeration cycle is being operated by both compression mechanisms, the displacement of the second compression mechanism is controlled by the second compression mechanism displacement control means by referring to an evaporator temperature detected by the evaporator temperature detection means and a second compression mechanism evaporator target temperature. The air conditioner can achieve required cooling performance as equal as conventional air conditioners can do, and variations of blown air temperature, room temperature, etc. can be suppressed by controlling cooling performance finely.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an air conditioner with a refrigerationcycle having a compressor for refrigerant, and more specifically, to anair conditioner suitable for controlling a refrigeration cycle having afixed displacement compression mechanism and a variable displacementcompression mechanism independent from each other.

BACKGROUND ART OF THE INVENTION

In conventional air conditioners, for example, in air conditioners forwork vehicles, there is a structure in which a compressor of arefrigeration cycle is operated by an engine to form an air conditioner.Further, in a case where a room space of a work vehicle (for example, aspace in a cabin) is large, or in a case where a thermal load variesgreatly, there is a case where a plurality of compressors are used for asingle refrigeration cycle and drive force transmission systems areprovided for respective compressors. Furthermore, there is an airconditioner wherein, in a refrigeration cycle having two compressors,one is a fixed displacement-type compressor and the other is a variabledisplacement-type compressor (for example, Patent document 1).

In a case where two compressors are used, however, there is a fear thata remarkable change of cooling performance occurs and variations ofblown air temperature, room temperature, etc. may occur by switching theoperation by both compressors to the operation by a single compressor inaccordance with variation of thermal load and the like. Further, whenthe temperature of an evaporator for refrigerant is controlled, althoughit is tried to achieve an evaporator temperature target value bycontrolling the variable displacement-type compressor at a condition ofoperating the fixed displacement-type compressor and consequentlycontrolling the total discharge displacement of the two compressors,because only one evaporator temperature target value is provided, it isdifficult to control the cooling performance finely, and also there is afear that a change of the cooling performance, and variations of blownair temperature, room temperature, etc. accompanying therewith mayoccur. Such an undesirable variation of cooling performance may cause acondition of too much cooling ability, and loss of consumption power,etc. may become great.

Patent document 1: JP-A-2003-19908

DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

Accordingly, an object of the present invention is to provide a controlsystem capable of achieving required cooling performance as equal as inthe conventional systems and capable of suppressing variations of blownair temperature, room temperature, etc. by controlling the coolingperformance finely, for an air conditioner having two compressionmechanisms wherein one is a fixed displacement-type compressionmechanism and the other is a variable displacement-type compressionmechanism capable of being changed in displacement.

MEANS FOR SOLVING THE PROBLEMS

To achieve the above object, an air conditioner according to the presentinvention has, in a refrigeration cycle, a fixed displacement-type firstcompression mechanism and a variable displacement-type secondcompression mechanism independent from each other, and has secondcompression mechanism displacement control means for controlling adisplacement of the second compression mechanism, compression mechanismoperation switching control means for switching to an operation by bothcompression mechanisms or an operation by any one compression mechanism,an evaporator for refrigerant for cooling air for air conditioning, acondenser for refrigerant, a blower for sending air to the evaporator,evaporator temperature detection means for detecting a temperature ofthe evaporator or a temperature of air at an exit of the evaporator, andevaporator target temperature calculation means for calculating a targettemperature of the evaporator temperature or the evaporator exit airtemperature. In the air conditioner, the evaporator target temperaturecalculation means has first compression mechanism evaporator targettemperature calculation means for calculating a target temperature forthe first compression mechanism and second compression mechanismevaporator target temperature calculation means for calculating a targettemperature for the second compression mechanism, and when therefrigeration cycle is being operated by both compression mechanisms ofthe first compression mechanism and the second compression mechanism, adisplacement of the second compression mechanism is controlled by thesecond compression mechanism displacement control means by referring toan evaporator temperature or an evaporator exit air temperature detectedby the evaporator temperature detection means and a second compressionmechanism evaporator target temperature calculated by the secondcompression mechanism evaporator target temperature calculation means.

In such an air conditioner, it is preferred that, when the refrigerationcycle is being operated by both compression mechanisms of the firstcompression mechanism and the second compression mechanism, a firstcompression mechanism evaporator target temperature calculated by thefirst compression mechanism evaporator target temperature calculationmeans is controlled at a temperature lower than a first compressionmechanism evaporator target temperature at the time of a sole operationof the first compression mechanism, and/or, at a temperature lower thana second compression mechanism evaporator target temperature calculatedby the second compression mechanism evaporator target temperaturecalculation means.

Further, when the displacement of the second compression mechanismbecomes minimum, or when the second compression mechanism is stopped,the evaporator target temperature may be used as a target value at thetime of a sole operation of the first compression mechanism.

Further, when the refrigeration cycle is being operated by bothcompression mechanisms of the first compression mechanism and the secondcompression mechanism and when the displacement of the secondcompression mechanism becomes a predetermined value A or less, it may beemployed that the displacement of the second compression mechanism iscontrolled minimum, or the second compression mechanism is stopped.

Further, it is preferred that, when the refrigeration cycle is beingoperated by both compression mechanisms of the first compressionmechanism and the second compression mechanism, the second compressionmechanism evaporator target temperature calculated by the secondcompression mechanism evaporator target temperature calculation means iscontrolled at a first compression mechanism evaporator targettemperature calculated by the first compression mechanism evaporatortarget temperature calculation means or more, and when the evaporatortemperature or the evaporator exit air temperature detected by theevaporator temperature detection means becomes lower than apredetermined value B, immediately the displacement of the secondcompression mechanism is controlled minimum, or the second compressionmechanism is stopped.

As the second compression mechanism, a variable displacement compressionmechanism controlled by a displacement control signal, or a variabledisplacement compression mechanism controlled by control of rotationalspeed may be employed.

EFFECT ACCORDING TO THE INVENTION

In the air conditioner according to the present invention, in the systemin that the refrigeration cycle is operated by two compressionmechanisms, when the refrigeration cycle is being operated by bothcompression mechanisms of the first compression mechanism and the secondcompression mechanism, a required cooling performance may besufficiently exhibited as well as the cooling ability may be finelyadjusted because controlled based on the evaporator target temperaturefor the variable displacement-type second compression mechanism, andfurther, in particular, variations of blown air temperature and roomtemperature ascribed to change of the operation condition of therefrigeration cycle (change at the time of switching between theoperation by one compression mechanism and the operation by twocompression mechanisms) may be suppressed extremely small. Further, byadjusting the cooling ability finely, it becomes possible to save theconsumption power.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic equipment disposition diagram of an airconditioner according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of calculation of secondcompression mechanism evaporator exit air temperature target value inthe air conditioner depicted in FIG. 1.

FIG. 3 is a diagram showing an example of calculation of firstcompression mechanism evaporator exit air temperature target value inthe air conditioner depicted in FIG. 1.

FIG. 4 is a time chart showing an example of control of the airconditioner depicted in FIG. 1.

FIG. 5 is a time chart showing another example of control of the airconditioner depicted in FIG. 1.

EXPLANATION OF SYMBOLS

-   1: air conditioner-   2: air duct-   3: introduction port for outside air or/and inside air-   4: blower-   5: evaporator-   6: refrigeration cycle-   7: main controller-   8: drive control signal-   9: first compression mechanism-   10: discharge displacement signal-   11: displacement control signal-   12: second compression mechanism-   13: condenser-   14: liquid receiver-   15: expansion valve-   16: evaporator exit air temperature sensor-   17: vehicle interior temperature sensor-   18: outside air temperature sensor-   19: sunshine sensor

THE BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments of the present invention will beexplained referring to figures.

FIG. 1 shows a schematic equipment disposition diagram of an airconditioner according to an embodiment of the present invention, forexample, an air conditioner for work vehicles. In air conditioner 1depicted in FIG. 1, a blower 4 for sending air sucked through anintroduction port 3 for outside air or/and inside air is provided at anupstream position in an air duct 2 opening toward a room interior (forexample, the interior of a cabin). An evaporator 5 is provided at aposition downstream blower 4 as a cooler for cooling air sent. Althoughnot shown in the figure, as needed, a heater core as a heater may beprovided downstream evaporator 5. The air having passed throughevaporator 5 and having been cooled is blown into the room interior.

A refrigeration cycle 6 with evaporator 5 is provided in theabove-described air conditioner 1. Refrigeration cycle 6 is constructedas a refrigerant circuit in which respective equipment are connected viarefrigerant tubes, and in this refrigeration cycle 6, provided are afixed displacement-type first compression mechanism 9 whose drive sourceis a prime mover (for example, an engine), etc. and whose drive iscontrolled by a drive control signal 8 sent from a main controller 7,and a variable displacement-type second compression mechanism 12 whosedischarge displacement signal 10 is sent to main controller 7 and whosedisplacement is controlled by a displacement control signal 11 sent frommain controller 7. In this embodiment, second compression mechanism 12is driven by an electric motor. In refrigeration cycle 6, a condenser 13for condensing high-temperature and high-pressure refrigerant compressedby first compression mechanism 9 and/or second compression mechanism 12,a liquid receiver 14 for separating the condensed refrigerant into gasand liquid phases, an expansion valve 15 for reducing in pressure andexpanding the refrigerant sent from liquid receiver 14, and evaporator 5for evaporating the refrigerant sent from expansion valve 15 and coolingthe air sent in air duct 2 by heat exchange between the refrigerant andthe air, are disposed in this order, and the refrigerant from evaporator5 is sucked into the above-described compression mechanism andcompressed again. The temperature control of evaporator 5 is carriedout, for example, by the control of a clutch provided on a drive forcetransmitting route from the prime mover to the first compressionmechanism 9 and a control signal for the electric motor for driving thesecond compression mechanism 12.

In this embodiment, to main controller 7, sent is a signal of anevaporator exit air temperature (Teva) detected by an evaporator exitair temperature sensor 16 provided as evaporator temperature detectionmeans for detecting a temperature of an evaporator or a temperature ofair at an exit of the evaporator (Teva). Further, signals from vehicleinterior temperature sensor 17, outside air temperature sensor 18 andsunshine sensor 19 are also sent to main controller 7, respectively.

In this embodiment, the control is carried out as shown in FIGS. 2 to 5.

When operated by any one of first compression mechanism 9 and secondcompression mechanism 12, the control of the evaporator temperature iscarried out by a target temperature of the evaporator exit airtemperature calculated by the evaporator target temperature calculationmeans. When refrigeration cycle 6 is operated by first compressionmechanism 9 and second compression mechanism 12, the evaporatortemperature target value control is carried out so as to providerespective independent evaporator temperature target values for thecontrols of the evaporator temperatures of the first and secondcompression mechanisms. This control method is shown hereunder.

The second compression mechanism evaporator target temperature at acondition where refrigeration cycle 6 is operated by first compressionmechanism 9 and second compression mechanism 12 is calculated, forexample, as a second compression mechanism evaporator exit airtemperature target value, and for example, as shown in FIG. 2, in acertain temperature region, it is provided as a variable valuecorresponding to an evaporator exit air temperature detected byevaporator exit air temperature sensor 16. In this variable region, ahysteresis can be given between the temperature elevating and loweringsides, and it is provided as a predetermined constant value in a regionexcept the variable region.

Further, the first compression mechanism evaporator target temperatureat a condition where refrigeration cycle 6 is operated by firstcompression mechanism 9 and second compression mechanism 12 is provided,for example, as a first compression mechanism evaporator exit airtemperature target value, and it is controlled referring to thedischarge displacement of the second compression mechanism, for example,as shown in FIG. 3. Namely, if the discharge displacement of secondcompression mechanism 12 is greater than a predetermined value A, thefirst compression mechanism evaporator exit air temperature target valueis controlled at a predetermined temperature B. If the dischargedisplacement of second compression mechanism 12 is the predeterminedvalue A or less, the first compression mechanism evaporator exit airtemperature target value is controlled at a predetermined temperature C.Where, the predetermined temperature C is higher than the predeterminedtemperature B.

Then, the second compression mechanism evaporator target temperature ata condition where refrigeration cycle 6 is operated by first compressionmechanism 9 and second compression mechanism 12 is controlled, forexample, as shown in FIG. 4.

In FIG. 4, the second compression mechanism evaporator targettemperature is calculated by referring to the evaporator exit airtemperature Teva, and referring to the evaporator temperature targetvalue, the discharge displacement of second compression mechanism 12 iscontrolled. Further, when the discharge displacement of secondcompression mechanism 12 becomes the predetermined value A or less, thedisplacement of second compression mechanism 12 is controlled at aminimum value, or it is stopped (in FIG. 4, shown as an embodiment forstopping). Where, the second compression mechanism evaporator targettemperature is higher than the first compression mechanism evaporatortarget temperature C shown in FIG. 3.

Further, when the evaporator exit air temperature Teva detected byevaporator exit air temperature sensor 16 becomes lower than thepredetermined value B (for example, 0° C.), as shown in FIG. 5,immediately the discharge displacement of second compression mechanism12 is controlled at a minimum value, or it is stopped (in FIG. 5, shownas an embodiment for stopping). Further, at that time, as shown in FIG.5, first compression mechanism 9 may be also stopped, and after apredetermined time passes (namely, at a stage where the temperature iselevated by the stopping), the first compression mechanism 9 may beoperated again.

When the refrigeration cycle is operated by the first and secondcompression mechanisms, the evaporator temperature control is carriedout by performing the target value controls of these both compressionmechanisms simultaneously.

By the above-described control, when the refrigeration cycle is beingoperated by the first and second compression mechanisms, a requiredcooling performance can be exhibited as well as the cooling ability canbe adjusted finely, and variations of blown air temperature and roomtemperature ascribed to change of the operation condition of therefrigeration cycle (change between the operation by one compressionmechanism and the operation by two compression mechanisms) can besuppressed. Further, by adjusting the cooling ability finely, it becomespossible to save the consumption power.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The air conditioner according to the present invention can be suitablyapplied to any refrigeration cycle having a fixed displacementcompression mechanism and a variable displacement compression mechanismindependent from each other, and in particular, it is suitable as an airconditioner for a cabin of a work vehicle violent in variation ofthermal load.

1. An air conditioner having in a refrigeration cycle a fixeddisplacement-type first compression mechanism and a variabledisplacement-type second compression mechanism independent from eachother, and having second compression mechanism displacement controlmeans for controlling a displacement of said second compressionmechanism, compression mechanism operation switching control means forswitching to an operation by both said compression mechanisms or anoperation by any one compression mechanism, an evaporator forrefrigerant for cooling air for air conditioning, a condenser forrefrigerant, a blower for sending air to said evaporator, evaporatortemperature detection means for detecting a temperature of saidevaporator or a temperature of air at an exit of said evaporator, andevaporator target temperature calculation means for calculating a targettemperature of said evaporator temperature or said evaporator exit airtemperature, wherein said evaporator target temperature calculationmeans has first compression mechanism evaporator target temperaturecalculation means for calculating a target temperature for said firstcompression mechanism and second compression mechanism evaporator targettemperature calculation means for calculating a target temperature forsaid second compression mechanism, and when said refrigeration cycle isbeing operated by both compression mechanisms of said first compressionmechanism and said second compression mechanism, a displacement of saidsecond compression mechanism is controlled by said second compressionmechanism displacement control means by referring to an evaporatortemperature or an evaporator exit air temperature detected by saidevaporator temperature detection means and a second compressionmechanism evaporator target temperature calculated by said secondcompression mechanism evaporator target temperature calculation means.2. The air conditioner according to claim 1, wherein, when saidrefrigeration cycle is being operated by both compression mechanisms ofsaid first compression mechanism and said second compression mechanism,a first compression mechanism evaporator target temperature calculatedby said first compression mechanism evaporator target temperaturecalculation means is controlled at a temperature lower than a firstcompression mechanism evaporator target temperature at the time of asole operation of said first compression mechanism, and/or, at atemperature lower than a second compression mechanism evaporator targettemperature calculated by said second compression mechanism evaporatortarget temperature calculation means.
 3. The air conditioner accordingto claim 1, wherein, when the displacement of said second compressionmechanism becomes minimum, or when said second compression mechanism isstopped, said evaporator target temperature is used as a target value atthe time of a sole operation of said first compression mechanism.
 4. Theair conditioner according to claim 1, wherein, when said refrigerationcycle is being operated by both compression mechanisms of said firstcompression mechanism and said second compression mechanism and when thedisplacement of said second compression mechanism becomes apredetermined value A or less, the displacement of said secondcompression mechanism is controlled minimum, or said second compressionmechanism is stopped.
 5. The air conditioner according to claim 1,wherein, when said refrigeration cycle is being operated by bothcompression mechanisms of said first compression mechanism and saidsecond compression mechanism, said second compression mechanismevaporator target temperature calculated by said second compressionmechanism evaporator target temperature calculation means is controlledat a first compression mechanism evaporator target temperaturecalculated by said first compression mechanism evaporator targettemperature calculation means or more, and when said evaporatortemperature or said evaporator exit air temperature detected by saidevaporator temperature detection means becomes lower than apredetermined value B, immediately the displacement of said secondcompression mechanism is controlled minimum, or said second compressionmechanism is stopped.
 6. The air conditioner according to claim 1,wherein said second compression mechanism comprises a variabledisplacement compression mechanism controlled by a displacement controlsignal, or a variable displacement compression mechanism controlled bycontrol of rotational speed.